High-temperature high-pressure properties of silica from quantum Monte Carlo

K.P. Driver
R.E. Cohen
Z. Wu
B. Militzer
P. Lopez Rios
M. Towler
R. Needs
J.W. Wilkins

Quantum Monte Carlo (QMC) is a highly accurate ab initio electronic
structure method which avoids approximating the exchange-correlation
potential as in density functional theory and provides benchmarks for
material properties. In this work, QMC computes high-temperature
high-pressure thermodynamic and elastic properties of silica,
including the phase diagram up to the core-mantle boundary. Results
provide the most well constrained equations of state and phase
boundaries available for silica, particularly in the deep lower mantle
where phase transitions of free silica could be partially responsible
for observed seismic anomalies. At the mantle geotherm, QMC predicts
the metastable quartz-stishovite transition occurs at 10(0.5) GPa and
the CaCl_2-alphaPbO_2-structured transition occurs at 100(8) GPa.